Asynchronous data interfaces are well known. An asynchronous data interface generally connects two systems such as a processor core and an external bus, where the two systems operate in independent time domains. In other words, there are two different clock domains, each domain having its own clock with different rates, frequencies, phases, etc.
In order to transmit data from one clock domain to another clock domain, the data typically needs to be synchronized between the two clock domains. One solution is to rely on a fixed frequency difference between the two sides of the interface to transfer a packet of data. A problem with this solution is that the frequencies need to be known in order to determine when data may be transmitted from one system to another. For the frequencies to be known, the frequencies need to be calculated, which requires additional system time and resources.
Another solution is utilizing data interfaces that use a single bit when crossing clock domains to avoid multiple bits being latched in different clock cycles. Once the single bit safely reaches the destination side, the full data width may be sampled. However, the single bit is not considered “safe” until metastability is resolved. Metastability is usually resolved by latching the bit two or more times in the destination clock domain. Once the full data width is sampled by the destination side, it must signal to the source side that data has been accepted. This is done by sending another single bit acknowledgement to the source side. In other words, the source side does not count a certain number of clock cycles before the acknowledgement is seen. Once the acknowledge bit safely reaches the source side, the source may drop the data and begin the process again with new data. A problem with this solution is that while it may work independently of clock ratios, it limits the writing of subsequent data until the current data has been read by the destination, which takes a certain number of clock cycles (e.g., 6 clock cycles) to complete.
Accordingly, what is needed is an improved data interface. The present invention addresses such a need.